A Goan-origin politician has emerged as a frontrunner to become Portugal's next prime minister after the country's main opposition Socialist Party chose him as its candidate for the 2015 elections.

Antonio Costa, known as the 'Gandhi of Lisbon' for his frugal lifestyle, has his roots in the former Portuguese colony in India where his grandfather was born and his father spent most of his life.

A popular mayor of Lisbon, the 52-year-old socialist was chosen as Portugal's prime ministerial candidate by the main Opposition Socialist Party for next year's polls.